Date: Tue, 1 Jul 2014 10:53:56 +0100
From: David Drysdale <drysdale@google.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Meredydd Luff <meredydd@senatehouse.org>,
        Kees Cook <keescook@chromium.org>,
        James Morris <james.l.morris@oracle.com>, linux-api@vger.kernel.org
Subject: Re: [PATCH 01/11] fs: add O_BENEATH_ONLY flag to openat(2)
Message-ID: <20140701095356.GC2242@google.com>
References: <1404124096-21445-1-git-send-email-drysdale@google.com>
 <1404124096-21445-2-git-send-email-drysdale@google.com>
 <87mwcuw2pj.fsf@tassilo.jf.intel.com>
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On Mon, Jun 30, 2014 at 01:40:40PM -0700, Andi Kleen wrote:
> David Drysdale <drysdale@google.com> writes:
> 
> > Add a new O_BENEATH_ONLY flag for openat(2) which restricts the
> > provided path, rejecting (with -EACCES) paths that are not beneath
> > the provided dfd.  In particular, reject:
> >  - paths that contain .. components
> >  - paths that begin with /
> >  - symlinks that have paths as above.
> 
> How about bind mounts?
> 
> -Andi
> 
> -- 
> ak@linux.intel.com -- Speaking for myself only

Bind mounts won't get rejected because they just look like normal
path components.  In other words, if dir/subdir is a bind mount to
/root/dir then:
  fd = openat(AT_FDCWD, "dir/subdir", O_RDONLY|O_BENEATH_ONLY);
will work fine.
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